In response to ever increasing energy demands and subsequent costs, a tremendous emphasis is being placed on energy-saving solid-state lighting devices in the form of light emitting diodes (LEDs). Specifically, a need exists for pure white-light LEDs as a more efficient replacement for conventional lighting sources. Switching to solid state lighting would reduce global electricity use by 50% and reduce power consumption by 760 GW in the United States alone over a 20 year period. Solid-State Lighting http://lighting.sandia.gov/; The Promise of Solid State Lighting for General Illumination, Optoelectronics Industry Development Association, Washington, D.C. (2001).
The complications associated with design and fabrication of such devices have generated great interest in developing white-light phosphors that do not depend on complex doping schemes or combinations of materials. One proposed solution is to use a mixture of semiconductor nanocrystals as the intrinsic emitting layer for an LED device. Achermann, M.; Petruska, M. A.; Kos, S.; Smith, D. L.; Koleske, D. D.; Klimov, V. I. Nature 2004, 429, 642-646; Mueller, A. H.; Petruska, M. A.; Achermann, M.; Werder, D. J.; Akhadov, E. A.; Koleske, D. D.; Hoffbauer, M. A.; Klimov, V. I. Nano Lett. 2005, 5, 1039-1044. Semiconductor nanocrystals can exhibit high fluorescence quantum efficiencies and large molar absorptivities. Alivisatos, A. P. Science 1996, 271, 933-937; Yu, W. W.; Qu, L.; Guo, W.; Peng, X. Chem. Mater. 2003, 15, 2854-2860. However, mixtures of such nanocrystals merely approximate white light by mixing the traditional red, green, and blue colors and result in a loss in total device efficiency due to self absorption for a device of more than a few monolayers. Mueller, A. H.; Petruska, M. A.; Achermann, M.; Werder, D. J.; Akhadov, E. A.; Koleske, D. D.; Hoffbauer, M. A.; Klimov, V. I. Nano Lett. 2005, 5, 1039-1044.
Therefore, there remains a need for methods and compositions that overcome these deficiencies and that effectively provide broad-emission nanocrystals having improved quantum yield.